Richardson's handbook of projection (1930)

MANAGKkS AND PROJECTIONISTS 1363 still it has the efifect of putting the wrong impedance across the secondary of the transformer. The jumper should, therefore, be used only in cases of emergency. An open transformer secondary usually results in loss of sound. Though occasionally the sound will come through, its volumn will be very low. You should have small difficulty in locating any of these faults, but if you are in doubt, examine the directions for dealing with similar circuits in the photo-electric cell amplifier. They will serve you perfectly. In the grid circuit of V2, anything that may happen will cause the current to deviate from normal, with the single exception of a short across R3 or R4, and the possibility of such a thing happening is so very remote that we may dismiss it as almost impossible of happening. We therefore may consider all the wiring of V2 to be OK if the tube draws plate current of normal value. A ground between R6 and the grid of V3 in the grid circuit is all that can happen in the grid circuit of that stage without affecting the reading of the meter. When the plate current of any tube reads high or low, the tube should be tested at once. This may be done by replacing it wTith a tube known to be normal, or you may test it in one of the other sockets of the 41 amplifier. If the tube is at fault, the reading will, of course, again be wrong, but if the reading on test be normal, then the trouble is not in the tube, but either in the wiring or some of the other parts of the circuit. In case it happens that all the plate current reads high or low, the trouble will be located in the plate supply, which is a part of the 42A, or else in the 42A amplifier itself. The plate current reading on the 42 amplifier will